This invention relates generally to injection molding and more particularly to a system in which several heated nozzles are releasably mounted on the side of an elongated manifold to inject melt through spaced gates to a common cavity, and a method of manufacturing the nozzles.
Injection molding is being used to make larger and larger components, particularly in the automotive industry. In addition to considerably increasing the size of the melt channel, this has led to the use of systems in which several nozzles extend from an elongated manifold through separate gates to a single cavity. These applications normally necessitate very high injection pressure up to 30-40,000 psi. and require very large molds which are difficult to machine with accuracy. In the past, the nozzles have been mounted along the forward face of an elongated manifold with sealing provided by each nozzle being in bearing contact against a shoulder in the mold cavity plate. However, in view of the large mold size and high melt pressure, it has been found to be very difficult to machine to the necessary tolerances to provide reliable sealing. Also in the past valve gated systems, as shown for instance in the applicant's U.S. Pat. No. 4,530,654 entitled "Injection Molding Peripheral Opening Core Ring Gate" which issued July 23, 1985, the melt flows through each nozzle in a channel around the valve pin. However, for the present high volume, high pressure applications it has been found to be more efficient to use a separate melt flow channel offset from the central valve pin bore.
Frequently, these large elongated cavities are non-linear and it is desirable to mount the nozzles in different positions relative to each other to connect to the manifold. The applicant's Canadian patent application Ser. No. 524,208 filed Dec. 1, 1986 entitled "Side Mounted Manifold Block for Variable Orientation of Injection Molding Nozzle" provided one solution to this problem using "manifold blocks". The applicant's Canadian patent application Ser. No. 529,897 filed Feb. 17, 1987 entitled "Injection Molding System Having Manifold with Side Mounted Nozzles and Method" discloses another solution to the problem in which each nozzle is bolted directly to the side surface of the manifold with the bolts allowing slight lateral movement between the manifold and the nozzle to provide for thermal expansion of the manifold. While this is satisfactory for some applications, it is time consuming to bolt each nozzle with a desired orientation and it is difficult to accurately align the inlet to the nozzle with the outlet from the manifold.
As is well known, it is essential to the satisfactory operation of an injection molding system such as this that the nozzles have suitable heat flow characteristics to provide substantially uniform temperatures along the length of the melt flow channel and the critical temperatures necessary in the gate area. While a method of casting a heating element into a manifold is disclosed in the applicant's U.S. Pat. No. 4,688,622 which issued Aug. 25, 1987, it is not directly applicable to nozzles.